1. Field of the Invention
This invention relates to a method of controlling the position and attitude of an end effector of a manipulator that has revolute joints.
2. Description of the Related Art
Various types of industrial robots have been developed to improve productivity and assure safety in factories. One type of prior art mobile robot includes an articulated manipulator. The articulated manipulator has an end effector at one end and is mounted on an autonomous carriage. The mobile robot handles an object or workpiece with the manipulator by controlling the travel of the carriage and the position and attitude of the manipulator.
The mobile robot described above includes a CCD camera or equivalent attached to the end effector to capture an image of the workpiece. The position and attitude of the end effector of the manipulator are controlled based on image data obtained by the camera.
The mobile robot performs the necessary control function in the following manner. The position and attitude of the workpiece is first derived from image data captured by the camera. Next, the robot calculates a target angle of each revolute joint of the manipulator necessary to shift the position and attitude of the end effector to grasp the workpiece. Then, the robot proportionally controls the angle of each revolute joint to agree with the target angles and the end effector grasps the workpiece.
The control method described above assumes that the workpiece remains stationary. The prior art mobile robot cannot adjust the target angles of the revolute joints responsive to the relative movement of the workpiece and the carriage to which the robot is mounted.